2000 DII, 4.0 V8 auto. 130k

I have an engine noise that I would not describe as knocking or tapping, something with more of a grind to it. It is rythmic and is the loudest at engine idle, it increases in speed with increased throttle, but only a little bit, as the sound goes away after only giving a little bit of gas. It is the loudest from the underside of the engine, I cannot point to a specific place as it seems to come just as loud from around the front as is does from the rear near the transmission. Although it does seem to be louder on either side of the engine. I have checked the cats to see if they were crapping out, and checked to see if the manifold bolts were secure. From what I can tell I don't think it is exhaust related. I have used a long screwdriver as a scope to try and pinpoint the sound, but to no avail. Any ideas?

Also, sometimes when I start the truck, I hear a sound kinda like a snort or grunt and can feel it through the brake pedal. Lately ive noticed that if I slowly push the brake it will go soft to the floor, but if I push quick they are nice and firm. I guess this could be the seals getting old in the booster.

Thanks for any help.

 

I wouldn't run that engine till you have someone check it out, any internal noise means there is damage going on while it runs.
Do you have a brake warning light on, how long has it been since you flushed your brake fluid?
Mike

 

No brake light on, I have not recently flushed the brake fluid.

 

Maybe grind was too harsh. The sound is really hard to describe. Maybe more of a light tap, but not like a ping of metal on metal....