Hearbeat Hum

[Heater Core]

Can't explain it any other way. Ya know how a normal engine just purrs along? Well now it sounds like a humming that beats like a heart beat. In Park and more so at 50-60 miles an hour and more intense going up steep hills.

Anyone know what might be causing this?

Of Note: I have another post "Only starts in Neutral" just before this one about the same vehicle, 1994 Olds Bravada, only starting in Neutral. I say this in case these two items might be related.

This is also posted as "groaning/humming noise" but I don't know how to delete them to make just one. Sorry. Anyway:

The exhaust gas pressure "puffs" to the heartbeat at the tailpipe?". Aside from the very loud deep slow heartbeat humming which is actually intermittent (when passing thru gears), when it is not "humming" it actually sounds like a constant loud deep version of a lifter knocking/ticking (inside the tailpipe as I said). I used the video on my camera to try to capture the sound but it can't be heard on camera audio (the ticking can but not the hum). Weird, considering how loud it is. I don't see where a video can be posted here anyway.

[Chris Stewart]

Does the humming change or can you feel it in the steering wheel while in a gentle curve?

[Heater Core]

Originally Posted by Chris Stewart

Does the humming change or can you feel it in the steering wheel while in a gentle curve?

No, you can't feel it. Just hear it. It gets slightly louder on big inclines; going up mountain sides (on highway). Faintly in Park and sometimes not in Park.

[Chris Stewart]

Easiest first,
If all the tires were installed at the same time, make sure you have 32 psi front and 30 psi rear.
While it's in "heartbeat mode", downshift to Drive which will cause the engine to speed up....does the heartbeat change?



You following this Eric?

[Leeann94astro]

^ Chris, my '93 Bravada says 35 PSI all the way around...

[ericn1300]

check your motor mounts, Chris had a quick way to check those visually if he can post it again. Other than that check the belt, pulleys, power steering pump and compressor.

[Chris Stewart]

My rear tires wear out the middle too quick if they're set the same as the front LeeAnn94astro...probably the heat and humidity down here.


Like Eric says,
To check the motor mounts, raise the hood, start the engine, apply enough brake pedal to hold your Bravada in place, put the gear selector in Drive, lightly apply throttle and look between the lower hood and cowl at the engine.
If you see it rock over more than a coupla inches, the driver's side motor mount is broken.
If it rocks over more than a coupla inches while the transmission is in reverse, the passenger side motor mount is broken.

[Heater Core]

I haven't had time til now to listen again. The heartbeat hum is actually coming out of the TAILPIPE. Yes, the tailpipe. I put my ear to it and it is actually coming from the tailpipe.

Vewy vewy intwesting. What ya think a that?

[Chris Stewart]

Does the exhaust gas pressure "puff" to the heartbeat at the tailpipe?

[Heater Core]

Originally Posted by Chris Stewart

Does the exhaust gas pressure "puff" to the heartbeat at the tailpipe?

Yes it "puffs". Aside from the very loud deep slow heartbeat humming which is actually intermittent (when passing thru gears), when it is not "humming" it actually sounds like a constant loud deep version of a lifter knocking/ticking (inside the tailpipe as I said). I used the video on my camera to try to capture the sound but it can't be heard on camera audio (the ticking can but not the hum). Weird, considering how loud it is. I don't see where a video can be posted here anyway.

[Chris Stewart]

My pics and videos are on Photobucket.com then I just post a link to there.

How'bout Tony DePillo's SS/B Honkin' Hemi ...

[Chris Stewart]

Almost sounds like a possible leaky exhaust valve.
Anybody remember how to diagnose a leaky valve with a vacuum gauge?

[PatrickinWA]

Just got a 97 bravada a few days ago and it was doing something similar. Just changed all the plugs and wires and it purrs like a kitten now. Looked like some one only did 5/6 plugs last time. Middle one on drivers side is a pain in the ass to even get the socket onto. I'll see if that fixs the cold start problem tomorrow. My sisters car had the only starts in neutral thing a while back. Neutral position sensor/switch was the problem and fix.

[Chris Stewart]

Thanks for the info and welcome to the site PatrickinWA!!!

[PatrickinWA]

Thought about this a little more today and thought I would mention the catalytic converter as a suspect since you said it gets worse on an incline. When they go bad the rust and whatever collects inside tends to just roam around in there so exhaust pressure builds up a little until it can push through.