Thanks orb, quite right.

Thanks Andrew. Only motd and b service a couple of weeks ago so assume O.K. Unfortunately no longer able to go under myself.

I'm not straddling them, going over bump directly. Not sure what else I can do.

What kind of car do you have?. MPV's don't generally have any more ground clearance than whichever hatchback they are based on.

even though I was very careful , very slow and smooth, on both occasions there was a horrible grating sound from the exhaust as the car went over. I drive an mpv so no low suspension.

If the noise was from the exhaust, is it hanging a bit low ? You might avoid the contact by aiming the wheels at the bumps instead of straddling them, as you are driving slowly ?

It could easily be the front bumper scraping the speed hump because people mostly brake just as they reach the speed bump, and as a result, the nose of the car drops.

Another possibility could be an underbody engine bay or sump cover that maybe not properly attached or that (even when fitted properly) hang down quite low.

Any suggestions to avoid this, other than don't go, welcome.

Get a car with higher ground clearance?

Difficult to see how the exhaust could scrape if is higher off the ground than the height of the speed bump. Could you perhaps have a broken spring or was the car heavily laden?

Mentioned mpv because not low suspension.

This is the second time you have said this, but as I said before, MPV's do not (in general) have any more ground clearance than a 'normal' car.

But regarding the actual speed humps, wear and tear will often result in a depression immediately in front and behind the hump as you approach it exacerbating the height/steepness. As the wheel drops down the other side, the compression of the suspension can result in contact being made with the undercarriage. If this is the case here, being an NT property, they may well not have the funds to fix it due to the reduced visitor numbers with covid.

In my experience there are not many speed bumps that do not have damage caused by gouging from passing vehicles especially those rubber ones that are bolted to the road. You see some vehicles going far to fast over humps, straddling them with one wheel and so on. There are some if on a strange road to the driver that are difficult to spot and in some pedestrian areas are a b***** nuisance.

Some places use "dragons' teeth" to enforce one-way operation - these clang when driven over correctly.