Humming noise coming from rear.

Hey guys,
I picked up a '95 300zx NA 2+2 auto recently. This is my first Zed. I have recently had a major service completed by the good gentleman at Dontex.

Since I picked up the car, I have noticed a pretty prominent humming noise coming from the rear wheels on both sides when sitting between 1500-2000rpm. This can happen in any gear. This noise only occurs when the car is in drive. I reported this to Dontex. They didn't notice anything out of the ordinary at the time.

I am hoping with so many Zed experts on here, can anyone help me out with this one? Is this normal and I am being overly cautious? It certainly doesn't sound normal to me.

 

Just doing some research and found this:

The initialization of the ABS actuator. This is a brief whirring noise that will come from somewhere behind your head when you just start driving. It comes on for abour 1 second after the car excedes about 5kph. It's perfectly normal.

However, I don't think this is it as it happens virtually any time I hit that rev range.

 

I dunno it could be a fat chick reading a cheese cake shop catalogue in the boot, mmmmmmmmmmmmmmm.

 

You said it only happens at 1500-2000rpm, this would lead me to believe if there is a problem it is engine or gearbox. I'm thinking this because if it is related to rear wheels, diff or drive shaft these all operate at a speed relative to the cars speed. Does that make sense?

If you rev the car in neutral with the car stationary and get the same noise this will also confirm the above. If not then perhaps you just have a rattle towards the back of the car that is excited at that specific rev range. Check the boot and spare tyre area for rattling items such as the jack and other tools.

 

mine has a similar noise i believe it is tyres

 

This noise does not happen in neutral, only in drive.

I have removed all the loose items from my boot this morning, and it is still happening.

My tires are brand new as well.

I will book my car in for an transmission service shortly. Hopefully this resolves the issue.

 

Drive shaft bearing. Check it out.

 

If it only happens when moving regardless of the speed but at fixed rpm range then its probably an exhaust vibration. It might be touching something.

Under you go with a torch!!

E

 

actually, you make a good point tassuperkart, I have been informed I am missing one of the insulators and covers on my right hand exhaust. Didn't think that might be reverberating.

Tassuperkart, mate, it's not true what everybody says about you!

 

just be aware, the rear bearings do eventually let go and are real expensive to source and a real PITA to replace and they only make a noise at certain revs as well

 

What - that he is a smart guy with brains and lots of old timer experience?
Its definitely true!

Get the torch out and get into that exhaust and watch those fat chicks - they can kill you!

 

Hawhawhaw.... The care factor attached to what some people think of me is zero!!

E

 

I will definitely have this looked at, along with the transmission as I am sure its time for a service. Thanks mate.

 

So I just had my car thoroughly looked over and had the auto serviced as well as a whole bunch of other stuff. The diff was checked, no issues. The problem however still persists. The auto was way overdue for a service.

I have also found that the problem persists ONLY when the car is in overdrive. By that, I mean that when the overdrive button is pressed, in any gear, the humming/chirping noise is prevalent between 1500-2000rpm.

Looks like I am going to have to get the proper pull apart done on the auto.

 

I know, I know - it's a budgie (google: "Budgerigar"), most commonly blue with white and black on it. Feel around down in the pockets either side of the spare wheel well (but be careful you don't get nipped). Typically they don't like that rev range and he's probably trying to communicate with the vehicle. Pretty common with Z's.

 

But that might be from you driving at the limit :br:

Chirping noises, doesn't take much. I get it now and then from my front strut brace.
If you get it at the rear then it could be something in the boot. Empty it out.

 

Is that going too far? Am I the only who assumed that FCT (forum name) is referring to her car?

 

lol thanks

 

I have emptied the boot. The mechanic is certain it is transmission related, as it only happens in overdrive on. I am going to have to take it to a "transmission specialist".

 

Diff

Have you checked or changed the diff oil? Might be low on oil or worn.