Resonating booming noise

That's the best I can describe it!

My 90 has the 3.9i engine and outbox from a Disco 1 fitted. As far as I recall, the Disco drove very nicely before it was broken (due to terminal rot in the chassis and bulkhead).

When I fitted the engine, I wasn't aware of an off-the-shelf exhaust, so I made one up from 2.5" parts from Jetex. It was nicely loud but not too bad, but I had what I can only describe as a booming resonance, like a vibration but it's mostly sound, if that makes any sense at all?

It was getting on my nerves and I thought it was the exhaust. I also found out that a TD5 exhaust would bolt straight up to the 3.9 headers, in the right place, so I bought a (cheap) TD5 exhaust, new, and fitted that. Well, that's the V8 sound gone!

But the resonance is still there. It's worse at low revs; if I hold it in gear up to high revs it seems to disappear, or at least quieten right down. It's quite loud tho in normal driving, annoyingly so really.

The engine and box are on rubber mounts, as you would expect, and I'm not aware of anything touching the chassis (or anything else) where it shouldn't. The exhaust is all on rubber mounts.

Anyone got any ideas on what might be causing it? If I can get rid of that I might put the Jetex exhaust back on.

TIA.

Has your back box fallen apart allowing sound to bounce about and reverberate...
Like my decat 4.6l, I made a couple of months back.
Between 2k and 2.5k rpm an unpleasant rumble started that vibrated my skull. New 2nd hand back box from old exhaust welded in and now a gorgeous sound that I get compliments about every day.
Bang your back box, if you hear anything inside swap it out...
Good luck.

Thanks for the reply, appreciate it. Pretty sure it's not that though. Both the exhausts I have had own it were brand new.

I've also been through the inlet system, tried it with/without the air filter, swapped the MAF out with a spare one, I even wrapped the elephant trunk hose in cling film in case it was letting in somewhere!

I'm starting to wonder whether it's one of the cats. The noise definitely seems to be coming from the driver's side, and although it resonates right through the truck, if I had to pinpoint a location, it seems to be worse under the driver's feet, so maybe that's the next thing to try.

Thanks again!

Can you put a video on YouTube? Then we can hear it

I've tried to do that a few times, both as a video and as plain audio, and for some strange reason the phone just won't pick up the noise at all!