Slight rattling under hood, which stops when you depress clutch and noise increases when shifting to 3th and 4th gear. Like the other authors, it sounds like the bearings are loose.

Took to a Pontiac dealer 2 days after the noise started. The mechanic said it is definitely coming from the transmission. He said it is normal wear and tear. He recommended driving it and only if the noise got worse to then replace the transmission. The noise is there but not really bad. He said you could drive like that for a long time and it may not get worse at all. To repair not worth it because of work involved.

Also said if we were to replace the transmission, we should might as well replace the clutch plates. Total estimate: $2300 for new transmission, $2-300 for clutch plates, minimum 10 hours of labor at $100 per hour. Yikes!!! The dealer said they will try and find a used transmission for us. Waiting on that quote. Will also take to an Aamco for second opinion.

Unfortunately it looks as though we will choose between replacing the transmission or the car itself.