olivia123 Posted March 19, 2011 Share Posted March 19, 2011 My 1999 outback has about 170,000 miles on it and has developed a rattle when you first accelerate and sometimes at idle. Heat shields was the first thought but they are all tight. The sound is coming more from the center of the car. I got under it and hit the rear catalytic converter with the heel of hand and heard the noise, sounds like something inside is loose. I assume there is no way to fix this short of replacing the converter. Is there any reason to fix this, I still have about 18 months to go before the next emissions test? I’m thinking I’ll just turn up the radio. Quote Link to comment Share on other sites More sharing options...
brycarp Posted March 20, 2011 Share Posted March 20, 2011 Sorry I'm not helping any with your problem, other than to "chime in" and say that I have concluded on my 1995 EJ18 Impreza that I have a resonance/buzz in my catalytic converter. In my case, it is most noticeable at about 2000 RPM, and fades above about 2200 RPM. I have a connection to a good muffler shop in my area, and I'm thinking at some point I'll check with them to see whether they can quickly fab a bypass pipe that would bolt in in place of the cat so I can confirm that that's where the noise is generated. I also at first thought "heat shields" and actually fastened them tighter a couple of places, but this sound wasn't affected. I also rigged a wire that hooked to the throttle and wrapped down around the front of the car so i could pull it to get the engine speed to the right spot to make the noise happen while I was under the car. That's when I determined that it seemed to be coming from the cat. I too have for the time being decided to just ignore it. It's not that bothersome, and while I'd like to get rid of the noise, I'm not finding myself highly motivated to spend the time/money right now to deal with it. Quote Link to comment Share on other sites More sharing options...
ScottG Posted March 20, 2011 Share Posted March 20, 2011 I had a similar problem with my '98 Forester. The front part of the converter shield was tight, but the rear section had lost its grip and was vibrating. I put 2 hose clamps togther & tightened them as much as I dared. Result: metallic rattles & vibration are gone. Be sure to check the pipe covers between the engine & the 'Y'. I found a couple of major vibrating rattles there. Hose clamps rescued me again. The older your Subie & the higher the milage, the more likely it is that the pipe or catalytic converter needs a few hose class. By the way, if you try to tighten the cover by loosening the cover bolts a bit & sliding shims under the section on the pipe, then re-tightening the cover bolts, *********edaboudid! The cover bolts are totally rusted 0n.(my 98 Forester has 193,000 miles on it & I'd drive it to California tomorrow, but the coveerter & pipe cover screws are rusted solid). If you want to actually remove any of these bolts, you'll wind up destroying the shield, trying to get those rusted recalcatrints 0ff. The only way I know to get rid of the bolts is to cut them off with an air powered die grinder or angle grinder. Best of luck finding & silencing that bothersome noise. Let us know the outcome of your work. ScottG Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted March 21, 2011 Share Posted March 21, 2011 (edited) The grid inside can break loose sometimes and rattle around. At worst the broken section can break apart into little bits and clog the exhaust system. If it is one of the front grid sections of the converter it can cause the converter to overheat and catch fire. If you don't have the funding to fix it right away, at least take it apart and gut the converter for safety's sake. Besides, it's fun! Edited March 21, 2011 by Fairtax4me Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted March 21, 2011 Share Posted March 21, 2011 Years back, I had an Audi with a rattling cat. I ignored it, only to have the loose cat material clog the exhaust pipe. It was so much back pressure that I could only drive the car 45 mph. It would go no faster. The bad part was that I was 300 miles from home, driving on a Sunday afternoon from Cleveland to Indy. Impossible day and time to find anyone to work on a car. I drove home mostly on the berm of the interstate, dodging road kill, with my 4 ways on, with cars and trucks whizzing by me on the driver's side. It was a most miserable trip that I will never forget. The only savings grace is that I figured out at the time that the cat was the problem, and was sure that the car would not stall out in the middle of nowhere leaving me stranded. Trust me, if you know for sure it is a bad cat, then replace it. A cat from a family owned muffler shop that does torch and weld, and pipe bending repair, will install a new one on the cheap. It would be well worth it. Quote Link to comment Share on other sites More sharing options...
MilesFox Posted March 21, 2011 Share Posted March 21, 2011 Do the hose clamp trick. that, or rip the heat shileds off. it is thin metal that gets rusty and falls apart. the inside of the cat failing is not as likely. Quote Link to comment Share on other sites More sharing options...
Allpar Mod Posted March 21, 2011 Share Posted March 21, 2011 I beg to differ. Heat shield issues are very common and quickly rectified by cutting them off. Internal problems do happen, as one board member already stated, and has happened to me (not on the OBW though). The grids can and will deteriorate and can fall apart. They will clog the system if not removed or the cat replaced. When I removed the one that I had this issue with, there was little left intact internally. From what the OP stated, it sounds more like he is having an internal problem with the cat. It needs replaced. Quote Link to comment Share on other sites More sharing options...
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