I have to agree, as its obvious when its dark outside. It probably happens all the time. I'm convinced its not related to the auto load levelers, as the problem is long after the car levels out. Might be related to the alternator. Who knows. GM was useless with me too. As per a prior post, the thunk in your steering wheel is probably the intermediate shaft. I had a lot of problems with them in my 02'*. I think I replaced 8 in 2 years(under warranty). For a while GM just greased them up until they found a fix. Known problems I have had with all my bonnevilles are window regulators, intermediate shafts, and now the load drag.

Add the blower motor at about 90K, both 02'*, and a retro fit with the new GM replacement

I agree, the compressor on the load leveler is not the cause. The "Hoover" vacuum cleaner sounding pump under the hood is my primary suspect.

I've read the threads of the thunk, had GM warranty "fix" on both of my '05 Bonnies, multiple times on each. It is obviously an engineering defect with space for the column length, GM trucks do it too.

That air pump is belt powered and wouldn't cause a amp draw or voltage drop. I think it is just a glitch having to do with Pontiac'* voltage protection circuit/PCM software for it. Something doesn't quite react in time or in step. Whatever it is, it doesn't seem to be a precursor to something going bad, or something we can alter.

The GXP doesn't have a belt pump, and I'm pretty sure most GMs are using electric air pumps now.... must have been a fuel economy move.

Wow, didn't even realize that one Z. Being nothing to do for these engines, I really dont go further than pulling the airbox cover to get at the NOS jets. We have had a few members mention them noisy. Everything under my hood stills purrs quietly @ 47K. Which is funny considering the paces I put it through. Whatever it is, it has been with mine from the beginning. I really stopped noticing it till this thread started.

I also assumed there were a few belt drives out there, but I looked at a bunch of belt routings on GMs, and it looks like they've been gone awhile.
Since the the air pump has to pump into the exhaust system for the cat reaction, there must be a one-way valve somewhere. It'* starting to make sense that the start-up back pressure to overcome the valve could cause a hi-draw.

Mine has been doing it since day 1. Dealer looked like a deer in the headlites when I brought it back. Of course these nit wits found nothing. It will do it about 1/2 mile to about 1 mile from cold sart up. I leave at 5am, so I see it every morning. I've never had any starting or charging issues. My battery is still original. Car has 36K.

I agree, Gm is clueless, and it doesn't appear to be a permanent damage issue. It must be common with the V8'*. My 02 SLE and 02 SSEi never had this issue. Looks like we'll have to live with it. Now that I've been more observant of the issue, it happens all the time, day or night, within 2-5 minutes of starting the car. I can hear it in the blower motor now(running slower for a few seconds).