On my D5 similar whistle noise was created by the balancing shaft inside the oil pan area (sounded like turbo whistle, makes you think that turbo is going). However to my knowledge they did not add balance shaft to D3, so might not be that, but maybe worth to ask from Volvo if your car has it. Mine was quite loud when coming to stop without breaking, but using engine break. There is an updated version out now and of course it is an expensive part. I just bought a new part and changed it myself in my garage. Very difficult to get instructions (mainly the bolt tightening torque). Rest is quite simple if a person has hands and wish.
https://www.google.com/url?sa=t&source=w...WJr2aLlxXb
Check from this thread
https://www.google.com/url?sa=t&source=w...WJr2aLlxXb
Check from this thread