Morris Minor Owners Club

Have a look see if the brake pipe is well clear of the rear propshaft coupling. This happened on my saloon some years ago but only with passenger(s) on the rear seat. It's amazing how much the sound was amplified through the bodywork.

Also (outside chance) check to see that the handbrake cables are not catching.

It may actually be the propshaft scraping - I've only heard of this once
Have a look at the diff - if the front end is slightly pointing upwards then you have a problem. In severe cases, the axle flanges corrode and it is possible that the whole axle rotates just a little.
If the front end of the diff points upwards then the prop shaft is too close at the crossmember, so when you go over a bump it fouls!
You will see a shiny ring on the propshaft where it goes through the crossmember.
However this is rare and there are a few other possibilities (some already mentioned)

Eye bolts on front suspension.

Does it make any difference if you are in neutral when you go over the bumps. Also wont do any harm just to have a look it case its something obvious.

that shouldn't make any difference anyway kev, because the propshaft is disconnected from the engine in the 'box if you are moving in neutral, so is the propshaft!

But in neutral there will far less torque going through it and if its not from the prop and rear end it will narrow down the possible causes.

the other thing it may be is worn rubbers on rear spring. the rear of the rear spring. those 2 support plates may be rubbing on the body. you may find rust around there.

is the mark shiny or old rusty. somtimes the mark comes from aligning the shaft up with the gearbox when being refitted for whatever reason. those marks are usually rusty. shiny will mean fresh contact.

how about shiny rust? ive got lots of that......

how much and does it come pre packed?

lol! when you grind old rust off, some doesn't come off and it goes all shiny....

can see is a mark round the drive shaft about half way down

The propshaft gets closer to the bodywork as the rear springs compress (over bumps / with weight in the car)
If it's a polished looking mark then this is going to be related to the noise, as it means the Prop is rubbing on something.

Where exactly is the mark?? If it is in line with the crossmember, then please see my earlier post regarding checking the rear axle / angle of the diff.
If the mark lines up with a bolt or something, The bolt needs to be moved or shortened. There shouldn't be any long bolts in the propshaft tunnel... However some people stick the mounts for modern type seatbelts there without paying much attention.

It looks as though you're going to have to get under the car, after raising and supporting SAFELY, to see what lines up with the mark.

i cant be rust if its shiny