306 1.9diesel Diesel knock

[pl509]

Hi... I've a 306d (non turbo) 2002 Estate, which has developed 'diesel knock'. First time not long after starting - then second time driving up hill after doing some 40 miles. Both times it happened - there was no unusual smoke from the exhaust only the louder rattle of the engine and increase in temp guage , more noisy on accelaration and under load... switching ignition off and restarting clears the fault!!!
The car starts first time in any weather and is good on fuel (upper 40's per gallon) and doesn't use any oil and it's done just over 100000miles. The only other noticeable fault it has... while driving at 30mph - sometimes you get a slight missfire or 'blip' in throttle where the engine hesitates then goes fine straight away - There seems to be a point in throttle travel where this happens.
I've had the car some 5 months - and otherwise seems ok. Any help would be handy - My brother in law is a mechanic and suspects the injector pump.