Hyundai accent loses considerable speed going up hills
 

I have a problem with my Hyundai accent manual diesel 03 reg. It was fine before but two weeks ago I started to notice that it loses considerable speed going up hills plus the revs would jump so high but the speed will stay the same or goes even down.

Firstly I thought it needs a service but despite changing oil, fuel filter, oil filter and air filter the problem still exists, may be a little improvement but same thing going up hill, the revs would jump so high and the speed remains same and very low. There is something I have also noticed and that is even on normal driving I can hear some sort of loud noise from under driving seat. It’s not like rattling or jumping but its something like grinding.

Any help is most appreciated and thanks in well advance