Yes, it was the diverter valve.
Had the control panel down while trying to find source of noise and the diverter valve fell out of its holding block. Looked like it was not pushed in correctly so clip that would engage at back wasn't connected.
Red circle is the block that diverter valve...
Worcester-Bosch Greenstar 30Si (G.C. No. 47 311 85 N.G.)
Had a new Flow Unit fitted as previous had developed a pin hole leak. Also topped up system inhibitor. Then this noise has appeared.
I'm going to checking if anything that is easily accessible is loose, but apart from that I could use...
Did your second attempt work jimbo84uk?
Having the same issue (not a kitchen) and wondering if I should exchange paint for silk version. As even after sanding previous coat I've suffered same cracking and bumps, just not frequently.
This has been on my to-do list for a long time.
If anyone knows vent style name or the potential manufacturer who made this style of vent. So I can source a replacement grill cover, if I ever get the screws undone.
The vent is less than 2 meters away from a drain access cover and has...