I had the same problem on my 850. The magnets have fallen off of the tweeters and are resting on top of the woffers (rear deck). This is part of the problem, also the voice coil is begining to sieze up on the woffers. Thus far I have replaced all speakers in the car with the exception of the rear deck. The front tweeters from Volvo lost their magnets as well. I have a set of Polk Audio DB 6930's to install but it requires cutting into the rear deck to fit and function correctly. Odds are, your speakers are due for the same treatment. Polk Audio EXII series component speakers (5250) work great up front with the tweeters in the OEM location as well as the woffer in the OEM door location. I posted a little thing on how to mount the front tweeters on www.swedespeed.com in the car audio section. The Polks sound great with the SC-810 and even better with the SC-816. BTW, the speakers in the rear door are Polk Audio EXII 5250a coaxial speakers. The task to replace all speakers took less than 2 hours, including the tweeters in the dash. There was no real modification necessary, just had to drill a few holes in some plastic. Be sure to use the hardware that came with the Polks when mounting or they will vibrate out.

Good Luck

Prospero