Multijet noise when warm?

[clockworks]

My Qubo Multijet has done less than 6000 miles, and had it's first service 3 months ago.
A few days ago it started making a tapping/chirping noise. It only starts when the engine is up to temperature (4 or 5 miles), and only while the engine is under load or at tickover - no noise on a trailing throttle or coasting in gear.

The frequency of the noise is related to engine speed, and gets louder when the throttle is wide open. When I switch the engine off, the noise sounds more chirpy for the last few revolutions.

My first thought (and the thoughts of my dealer) was a sticking hydraulic tappet, but why would that only start once the engine was up to temperature, and stop on a trailing throttle?
A Post Office mechanic friend said he's heard similar noises from the MJ engines in their Vauxhall vans, and failed alternator clutches are common.

Given the way the noise starts as soon as the temp gauge reaches the normal position, and only happens when the injectors are passing fuel, I'd be inclined to think it's an injector or water pump related problem, but I'm struggling to find a link between the two conditions.

My dealer added some "engine cleaner", and said to run it over the weekend and see what happens. There's been no change. His next action will be to strip the hydraulic tappets, but I think that's not going to help - can't see why a noisy tappet would go quiet on the overrun.

Any thoughts?

 

[impulsivearies]

My car has developed the same noise after two years and 28,000 miles.
Have you been able to resolve your problem?

 

[buster]

I run the bigger MJ,s- 1.9 and 2.4.Ive had funny noises to.These turned out to be the crank damper pulley.But is this a diesel knock?Perhaps its something to do with the engine temperature sensor,thus the temp reading that the EDC is seeing is wrong,and therefore the timing and mixture is not backing off once hot.