When going over bumps or holes in the road my car occasionaly makes a heavy thudding noise, sometimes its as if the engine could come through the flaming dashboard. strange thing is is that it doesn't always do it, its as if at times when you go over a bump it catches the car expectantly?? Engine feels a little unstable to inside the bay when turning on/off. 

Just wondered if any of you experts out there had any ideas as garage is now closed until next Thursday. Just had gearbox mounting replaced underneath car for £45 and this hasn't made much difference. The front arms, shockys springs all appear to be ok..

Car has done a high mileage of 250,000 however the engine still pulls great as its 1.8tdci and I was hoping to keep car until April isshh.

So any advice is very much appreciated as its always good to have an idea of what it could be before I go garage.

Cheers in advance and have a good one over Xmas.

Could be a few things , worn shocks springs but that would not make engine shake , you have engine mounts drivers side pass side and lower gear box mount which you changed , it could be one of the other two , bumps and knocks while driving are normally suspension and bush related it's hard to say without testing it could be steering rack related lower arms  drop link  top shock mounts or could be a loose undertray I've had an unsecure  battery baffle a customer for months till we found it rattling about in engine bay for him , get it on a two poster it's the only way to check really . 

Cheers