Very strange noise

Hi guys,
I've got the strangest noise coming from my defender. It only occurs when I'm going about 30-35 in 4th and 5th gear. The noise is a sort of low growl as of there is some sort of sheet metal piece rattling but I can't see why it would only happen at this speed? There is also a vibration at the same time as this noise on the drivers floor. I've looked under for anything loose but I can't find anything.
Cheers, David.

UJs? They make some right funny noises when they are gone.

Loose exhaust? Mine grumbles but a kick every now and then fixes it for a few more hundred miles.

Don't think it's the uj as I had that off a few weeks ago and it was fine although I suppose there's no harm in trying. I'll try the exhaust as well, do you think it would just be the rubber hangers that are gone or maybe something inside one of the silencers that's loose?

Just a quick check,
Wheels straight, look at the rear track rod that goes wheel to wheel, where it passes against the diff check it's not bent out of shape ever so slightly and rattling against the diff catcher..
Happens all the time

I have no idea why my exhaust rattles. It doesnt do it enough for me to check. I would imagine either a rubber has gone or the bracket holding it. Pretty obvious sound though. Take middle seat/cubby box out and drive with cover off. Might help locate noise. Ive had centre console & sound proofing removed on my disco for months now and its helped me no end rule out certain things.

Air filter housing ?

When low (sub 1k revs) in 3-4-5, my air filter housing rattles,

Only cause the brackets gone on one side,