Boiler sounds like a plane plumbing advice

Boiler sounds like a plane Can anyone advise why my Worcester Bosch System boiler when heating hot water does this sort of surging/woosh/hum that's a slightly higher pitch than the normal water heating noise noise like a plane taking off every 5 to 15 minutes? It last about 10 to 15 seconds each time. It's very noisy and our old plumber who dealt with our boiler is no longer in business so even though it has done this before we can't remember what it is. Boiler is regularly serviced. Thanks in advance.

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