Loud high pitched squeal ONLY on deceleration
 

My 2000 Boxster (2.7L) with 93000 miles just developed a loud, high-pitched squeal that ONLY occurs during deceleration (braking or taking foot off accelerator). It stops when the car is at a full stop or is accelerating. This sound does not appear when the car is first started -- it appears after the engine has warmed up or after 8-10 miles of driving. There is no change in the squeal with the HVAC on or off. It feels like the sound is louder on the passenger side. What may be failing?

This could be an Air Oil Separator issue, the squeal could be air being drawn past oil filler cap into the engine, I had this noise last week, also had smoke issues which pointed to AOS, had the AOS changed and all is now well

Excellant description of the problem Judy, I agree it could be a AOS gone bad. It can cause this noise from the front or rear engine crankshaft seal also. Removing the engine cover behind the seats will allow verification of a front seal air leak or might be best to replace the AOS if it has not been done before.

Thank you!
 

It's reassuring that two of you are in alignment of what might be the problem. Whew. I'm pretty sure, based on my repair records that the AOS is not something that has been replaced so it "sounds" like it's time to check that out. Thanks so much!

Thank you, that WAS the problem!
 

Thank you to BYprodriver and k9dbm for suggesting that it was the AOS. It was!

It was remarkably easy (5 minutes) to put the soft top back 18" into "service mode" and remove the soft and hard covers over the engine to get to the engine. (Seems there is a set of DIY photos or videos for everything!) Bought & had the $114 AOS over-nighted from PartsGeek (best prices/best turnaround time).

Only had to remove the right back tire to get to and replace the AOS (for the 2000 model). (Another DIY video) It took me a total of 2 hrs but I'm just a curious woman not a trained mechanic!

Boom, problem solved! Quiet & smooth again, yay. Thank you to BYprodriver and k9dbm on this 986forum for helping a woman determined to fix it if all possible herself to DO JUST THAT for $114!

Well done all around! Searching these forums then posting a question if needed with all pertinent details goes a long way to solve just about any Box problem.

Merry Christmas! :D