March 25, 200422 yr Looking for the cause of a medium pitched humming noise coming from my air intake system. Let me give you the background. I recently had a water pump replaced on my 97 OBS at the Subaru dealer. The next day I had a full fuel system cleaning performed at Valvoline Instant Oil Changes. This cleaning consisted of disconnecting the fuel system and connecting a cleaning fluid canister to the fuel intake. Simultaneously they were performing an engine oil flush. I also had all the differential fluids and manual transmission fluid changed at that visit. I also had them change the oil with their new Valvoline MaxLife. The next day I noticed a medium to high piched humming coming from my engine compartment. It is imperceptable to most people but I noticed it right away. It does not seem to change pitch or go away with acceleration but I cannot be sure about this because road noise usually drowns it out. I traced it to the air filter compartment. With the engine running I removed the air filter and the noise became much louder and a little lower pitch. I took a quick look at the vacuum hoses and could not find a problem there. I am also not sure if the noise was there after I picked it up from the dealer of if it only started after the Valvoline work. If anyone has any suggestions on what may be the source of my problem please reply. Thanks.
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