Grinding sound from under

Hi all,
gonna have a hard time describing this but here it goes… early today I noticed the brake pedal traveling lower than usual and feeling mushy. It’s taking longer to stop. After reading many threads here, I suspect a bad master cylinder. Not brake work done recently. But that’s not what’s worrying me. At first I heard a faint grinding noise from (what I thought was) coming from one of the front wheels. Arrived at my destination and after a while started it up and drove off again then the grinding was louder and I felt it… very pronounced from under the truck. Arrived at next destination…. Later got back in and drove off and the grinding was even louder. It only happens for a short time (3 seconds maybe) and only after the truck has had time to sit. If I turn it off/ right back on and drive it will not happen.
could this be related to the brake issue? I recently did a tune up my self: plugs, coils, air filter, pcv, 3 belts. Any input is greatly appreciated.
2004 pre runner 190k miles. Had a brake fluid change 2 yrs ago.

 

No brake work done recently. It only happens after the truck cools off a bit… and when I first start driving. It’s almost immediately after I start driving. A quick 2-second grinding noise that can be heard by others around me. Never happens again while driving. Def coming from just behind the firewall.

 

I had a wheel bearing start to go bad once that did just that, grinding nose and then my brakes started to feel like they were going out.

 

Take the front wheels off and inspect your brake pads and rotors!

 

I also had a wheel bearing going out....mine you could hear the rotor starting to rub the pads when going slow around corners....

 

First - Lift the front end off the ground and try and push the wheel side to side to see if there is any side to side (relative to truck) movement. If there is any play, what so ever, your wheel bearing is bad.

Second - Take wheels off and inspect your pads and rotors.

 

Is your brake fluid low? If so and no leaks id guess your pads are worn

 

I’ll def check pads and bearings. But If this were a brake pad or bearing issue, wouldn’t the grinding happen all the time… or more often? This is only happening after I start the truck and start moving for the first time. It doesn’t happen again After that. Not after green light, not while driving distance or turning, etc.

the brake fluid is a hair low. Not at min, but not max. Right in between. Gonna top it off and see if that matters.

 

Topped off the brake fluid. Drove it all day. Didn’t make a difference.

 

update:
drivers front has a very slight wiggle but barely noticeable. all others are fine. no wiggle at all. front brake pads are not new...but still got plenty of meat on them. rotors look good also. grinding noise is still there, but now its a really quick grinding... like 1 sec... then stops. but again, its very pronounced and i feel it in the gas and brake pedal. sound to be coming from directly behind the firewall. looks like ill have to live with it until something breaks and reveals the source.

 

Or just do some proactive maintenance and fix the problem. If it's bearing, and you just keep driving it until it breaks you probably won't have a truck to fix afterward.

 

Very true. Made an appointment to have it checked. Although… the grinding has stopped. All I did was top off the brake fluid. It wasn’t even that low. Brakes feel normal again also.