I have had the same turbo problems, it sounds like you may have a leak in one of the hoses, but if there is a noticible whine your turbo is probably on the way out. If you are going to continue to drive the car, you should try to baby it. I drove my 86 760 wagon for a long time with a whining turbo. I tried to avoid boost, especially accelerating from stop, it is not that hard if you get use to it. I believe my car went through turbo's because they were lousy rebuilds. I always warm it up and cool it down and change the synthetic oil every 3000, yet the last turbo went prematurely. I bought a NEW turbo center cartridge from IPD (www.ipdusa.com)for about $500. As long as the housing isn't cracked and you don't hear a grinding noise yet you can by the center cartridge only. If it's too late your probably looking at $1000. If you are bringing it into a shop probably at least $2000. Make sure you get a good rebuild by a reputable shop if you go that way.

Good Luck !