info needed please

Hi, i have a 97 300tdi with 64000 miles and full service history(well up untill i bought it at 47000 last year). I have the car regularly serviced by a mechanic friend(who has now moved away). I was wondering if anyone could tell me why when i back off the accelerator then go back on it the car seems to hic as if you are in too high a gear. this can happen from crawling speeds right upto motorway speeds.Any ideas or suggestions would be greatfuly received as it is really starting to annoy me(people probably think i am learning to drive lol).
thank you in advance
martyn
p.s it only lasts a few seconds