I found one Technical Service Bulletin from GM concerning noise in the motor. I do not know if your car is affected by this TSB or not, but you may want to have Buick check it out in the air on a lift when it is cold just in case. If this does not sound similar to your condition, do not click accept. We want to do you a service first. Review the TSB and see what you think. Thanks.
This bulletin is being revised to update the model usage and parts information. Please discard Corporate Bulletin Number 06-06-01-014 (Section 06 -- Engine/Propulsion System).
Some customers may comment on a ticking or knocking type noise coming from the engine or transmission area.
Typically the noise is caused by either the transmission rear dust cover contacting the flexplate (refer to Corporate Bulletin Number 05-06-01-028) or a cracked flexplate.
With the vehicle raised and supported on a suitable hoist, verify that the noise is coming from the flexplate area. If the noise is present, follow the procedure below. If the noise is not coming from the flexplate area, refer to Lower Engine Noise, Regardless of Engine Speed in SI.
Important: The following information only applies to vehicles with the noise coming from the flexplate area.
Important: Only proceed to the next step if crack(s) in the flexplate are found.
Important: Steps 11 through 16 only apply to the 3800 L26, L32, L36 and L67 V6 engine. Proceed to Step 17 for all other applications.
Important: Step 17 should only be performed if the dowel pin hole at the 2 o'clock position is NOT out-of-round.
L26, L36, L67