Engine rattle/rumble

Thank you for you warm welcome. I have just one issue at the moment. When at idle there is a rattle or rumble sound from I think the rear of the engine. You can also hear it inside the car with the doors shut . The rumble is constant and does not appear to speed up when increasing the revs. I questioned the previous and only owner and his reply was that the 3.8 supercharged was a noisy engine. The car has been well looked after and regularly serviced and now has 149.000 miles. Any ideas please?
Len

The exhaust system has a flex joint right behind the engine and near the firewall.
If that starts to go bad it can make a slight exhaust rumble before technically failing. It might be the cause of the gradual increase of noise in that area.
Can't be certain without listening to it though.

Hi Len,

Other ideas - could be a bad supercharger coupler or idler pulley. Run it with no belts (not for very long as there is no water pump during this test) and see if it gets quieter.

Yeah, the 3800 is not a noisey engine lol. What a dumb shit previous owner. That remark is called ignorance . Does the rattle sound like a can of rocks? When you accelerate does the sound go away? The S/C coupler has a nasty habit of going bad.

Hi Scott. You hit the nail on the head, a can of rocks is the sound right enough. I thought his reply was rather odd. BTW I have just found out that the exhaust input and output gasgets are leaking coolant . The coolant has also been mixed with the green stuff. I will address both problems asap as cash flow permits. Thanks.
Len

Lenrapkins wrote:

Hi Scott. You hit the nail on the head, a can of rocks is the sound right enough. I thought his reply was rather odd. BTW I have just found out that the exhaust input and output gasgets are leaking coolant . The coolant has also been mixed with the green stuff. I will address both problems asap as cash flow permits. Thanks.
Len

Not quite sure I know what you mean about the exhaust gaskets......exhaust gaskets should never have coolant in/on them. Are you talking about the Lower Intake Manifold gaskets? Another nasty habit of GM V6's is the LIM gaskets go bad. They have an updated gasket to resolve this issue. Unfortunately, most ppl never know that they are leaking until it starts running bad, or the coolant starts mixing with the oil.

Len,
You did mention that you had 149K miles on the car/engine.

It is time to replace all of your Lower Intake Manifold gaskets or else you will have some serious engine trouble.
Especially after mentioning that you are loosing coolant from some gaskets. Can be the notorious LIM gaskets and I recommend you have them changed out immediately, but only if you use the new and revised GM aluminum gaskets.
The gaskets from the parts store are not made the same and will not last as long as the newer GM gaskets.
Read the "Write Up" on LIM gasket change and ask any questions you may have. That write up lists all the P/N's of the gaskets required to do the job.
Even if you are paying someone else to do the work, you need to convince them that you need to buy the gaskets from GM for them to do the job.
While the SC is off to do that job you can remove the SC Snout and replace the coupler, another part that you will need to buy from one of the vendors listed on here, ZZP is one that comes to mind. Also buy 8 oz. of GM Supercharger fluid, as that will be needed to swap the coupler out with a new one.
Keep asking questions and reading what is available on here for technical info.
Good Luck

I just replaced the coupler on my setup and it has almost identical mileage to yours. It killed all the gravely/rock tumbler noise the car was making. My supercharger was pretty quiet up until 10,000 miles ago and then it got LOUD. It sounded like a rumble at idle and actually would make noise a bit with throttle.

HTH

Lenrapkins wrote:

Thank you for you warm welcome. I have just one issue at the moment. When at idle there is a rattle or rumble sound from I think the rear of the engine. You can also hear it inside the car with the doors shut . The rumble is constant and does not appear to speed up when increasing the revs. I questioned the previous and only owner and his reply was that the 3.8 supercharged was a noisy engine. The car has been well looked after and regularly serviced and now has 149.000 miles. Any ideas please?
Len

The PO is fibbing, and you can refer him/her to me for discussion if appropriate.

Based on mileage and what you're stating, you've got to replace the lower intake manifold gasket and the supercharger coupler. GM dealers will not, in practice, replace the couplers but you can do it yourself or have an independent mechanic do it for you, it's time consuming but not difficult. Same for the LIM gasket, timeconsuming as there is much to remove but it's another hand-tool job.

Recommendation - get the upgraded replacement LIM gaskets (NAPA would be a great source, or rockauto.com, or a GM dealer) and a coupler (try darossillc.com). If you have a press consider also getting replacement bearings for the supercharger (darossi has those too). There are writeups on this site for doing the coupler and the LIM; reading thru them it will be easy enough to combine them to do both for a DIYer on a day, 1/2 day for a skilled mechanic would be my guess.

The noises are probably why the PO ditched the car. Your gain.

Albertj