Hello, I am new and confused and also not car savvy so please bear with me!

I have a 2004 Subaru outback that has transmission issues. The check engine/cruise control lights are on all the time and I've been told by the previous owner (my parents lol) that it needs a new catalytic convertor. I've had this car for about 8 months and it drives great despite the impending engine issues. However, over the past month I have been hearing this vibration-like sound near the driver's side front wheel well that just sounds like metal on metal at exactly 175 rpm. It only happens on acceleration and is not turning-dependent nor does it affect the steering wheel or driving whatsoever. It's just a loud friction noise at relatively low speeds.

I should note that I had a look at it to try and diagnose the issue and all the basic hardware underneath is tightened and it is not the same sound of a bad CV axle that I've been listening to all over Youtube

 

Also, if anyone wants to tackle my transmission problem that would be useful, I find it hard to believe my car runs this great (responsive engine/never overheats) when I've been told the catalytic converter needs replaced.

Edited March 15, 20206 yr by brt49845

Auto or manual transmission? How many miles?

Does the sound go away if you step on the brake? 
Does the sound occur if car is stationary?
Is it by any chance a loose heat shield on the exhaust rattling?

What are the transmission and/or catalytic codes/issues? Did you get the codes read? The catalytic converter code is usually P0420 and while you can throw your wallet at the car, results may vary. 

Edited March 15, 20206 yr by brus brother

38 minutes ago, brt49845 said:

hearing this vibration-like sound near the driver's side front wheel well that just sounds like metal on metal at exactly 175 rpm

i do hope you mean 1750rpm - the car wont be running at 175, lol

but anyway, yeah, check heat shields on the drivers side of the car

as for the codes, you need to find out what exactly they are, and the order they appear in. this can often point you i the right direction of what needs attention first.

i sincerely doubt that the cat needs replacing if it is running & driving as well as you say. clogged cat would cause all sorts of drive-ability issues

38 minutes ago, brus brother said:

Auto or manual transmission? How many miles?

Does the sound go away if you step on the brake? 
Does the sound occur if car is stationary?
Is it by any chance a loose heat shield on the exhaust rattling?

What are the transmission and/or catalytic codes/issues? Did you get the codes read? The catalytic converter code is usually P0420 and while you can throw your wallet at the car, results may vary. 

Automatic transmission with 138,000 miles and it only makes the noise while driving, the heat shield doesn't move when I tried shaking it but it does sound like the noise that would make.

You need to bang around on the heat shields as they don't have to move much. 

The reason I am suspect is the sort of harmonic vibration that would happen under certain rpm/load.

My 05 Outback exhaust is a bunch of stainless pool hose clamps holding it quiet.

1750rpm is EXACTLY where both of our  Foresters’ exhaust manifold/collector heat shields arrived at optimum harmonic frequency; -in other words ‘rattled their loudest’.

Remove them, wedge them or somehow fix them and all should be good.

 

Edited March 18, 20206 yr by Mitchy