Noisy potterton performa 24 (not he)

[pil]

Always a bit of a vague one to pinpoint via the web but worth a try with the experience on here.
Boiler has just started making a noise when switching on, appears to happen with both DHW and CH operation.
On first switching on, pump starts to run, then fan, then igniter and the boiler fires up. After 5 seconds what I thought sounded like the fan going out of balance or the bearing failure starts. It appears around the house to be louder than it actually is at the boiler, but from outside the house the fan operation sounds no different to normal. It would APPEAR to be coming midway up the boiler, possibly around the heat exchanger. Certainly not at the top or bottom anyway! Would this sound feasible and if so would a flush be worth a try before going deeper?
Also worth noting, when the boiler thermostat operates and the pump continues to operate the noise goes then returns on the next cycle but only for a few seconds!!
Like I say, long shot but worth asking

 

[AGAS]

why do you want to have a flush for a proposed fan problem ?? have had BG looking at it by any chance

 

[pil]

Harsh! Maybe didn't word it properly, but what I meant was the pump and fan both appear to be fine (assuming if it were the fan making the noise it would be heard from outside at the flue and also when coming in at the start) it was more a comparison to try to describe the noise......

 

[AGAS]

wasn't meant to be harsh , try and post a video of the noise

 

[pil]

Not harsh on me, meant harsh on BG ( didn't say it wasn't deserved though) Tried to video it but can't really pick it up on the phone. More I listen the more I think it's water flow related though