Isolate Noise to Potentially Diagnose Issue

This is a 99 Tacoma with a 33rz I4 2.7l. It's 5spd manual, 4x4. 340+k miles.

Need help figuring out what a couple of noises are when driving the truck.

1. A noise that sounds like thin metal bouncing / rattling inside a metal box only under heavy acceleration. It's clear as day from the cab with windows down. Sound horrible. It's not coming from the engine. I've been through that and measured valves. The engine looks good other then 340k miles on it. It sounds like exhaust. It's only under acceleration with load. If I had to guess it's either a O2 that's blown up or catalytic converter is falling apart, but wanted to get other input. I'll hopefully check the O2's here soon. Looks like each O2 has a 2 x 10mm bolt. Checking the converter is going to a bit more effort and probably easier to just put money into a new exhaust.

2. Another noise is matching wheel speed. It's coming from the back of the truck. I pull the rear drums off and the brakes look normal. The wear on the pads don't look off. I spun the axles and they don't seem off at all. I still need to try the wiggle with the wheel on, but no noise that I recall at this point. However, it sound horrible when accelerating or braking. When cruising at speed there is no noise at all. Slightly worried it's pinion bearings. Never replaced one of those, but sure I can figure it out. Just wanted to know if anyone knows.

Let me know any question that might help or things I can check to narrow things down. Appreciate the time.

 

I realized I put this in the wrong Gen forum. Can someone move it or do I delete and repost?

 

For the exhaust rattle, get under the truck and lightly tap it with a plastic hammer or something similar. You should be able to figure it out that way. Also wiggle your heat shields, one of mine is loose, I just haven't yanked it off yet.

 

Cool, I'll give that a go. I've been under there wiggling everything I can with my hand but the idea to use a rubber hammer never came to mind.

 

It's a trick I learned years ago for diagnosing bad cat converters. You'll hear all of the innards shake around if they're breaking down.

 

Got out there and hit the exhaust several times and the catalytic converter sounds like a penny is bouncing and settling at the bottom. So definitely have to replace / solve that one. Looking at the bolts on the exhaust, looks like it's the original bolts from 340k miles ago. They appears like they rusted into one piece with the rest of the muffler system. I'm guess the only way to get it out is to do one of the following:
- gator saw the bolt heads and drill out the threaded section, then put a replacement in.
- Take it to a shop for them to do it
- Replace the exhaust system since it's wore out and put a nice system in?

The last one won't happen today, but maybe later this year. I'll likely put in a replacement straight pipe if I can tear out the old bolts with reasonable force. But not sure if that will end up being any better then just replacing the whole thing. I still have to figure out the other noise, maybe lift up the back end and unbolt the drive shaft then give it a spin to see if the pinion or axles are loose / grinding?

 

You could also have some place like Midas cut and weld in a new exhaust flange there. I have to have that done on mine sometime soon.