I have come to the experts and wondering if anyone can help. My 2005 V50 has 62K and at the end of last week started making a whistling sound when I removed my foot from the accelerator. It went in for service yesterday (with a mechanic that I COMPLETELY trust! He has never let me or anyone in my family down in the 20+ years we have been bringing cars to him):
1. when I described what was happening he immediately said “sounds like a vacuum leak”
2. when he ran the code it came up as mixture issue between oxygen/gas mixture
3. he ran the smoke test to make sure, the test came up with no leaks.
4. He checked the exhaust system when the car was on the lift. All clear.
5. He checked the alternator, all the spark plugs, and intake manifold. All clear.
6. After a test drive he did another smoke test thinking that the car needed to run, same results no leaks.
7. No problems during idle, no stalls or high revs.
8. After a bit of a delay between turning of key and turnover of engine at cold start. But then quickly comes down to normal idle

Here are the symptoms:
1. as soon as I remove my foot from the accelerator the whistling starts.
2. The whistling sound is somewhere on the drivers side.
3. there is a slight vibration on the driver’s side when car is stopped. I can feel it
through the seat.
4. when over 55 mph and I release my foot from the accelerator, no whistling.
5. Good 5 secs. of whistling after turning car off.

Anyone have any clues?!?! Ever hear of this happening??? I really don't want to take it to the dealer and pay dealer prices, but I think this is my only option. Please help!!
Thank you for any help, suggestions, ideas, or any words of encouragement:)