Airflow Aventa in-line extractor interference

[kered10]

My bungalow had a bathroom refit 9 months ago, including the above fan mounted in the loft. 6 months later, we had the 2nd shower room refitted - another fan loft-mounted on the same timber shelf on the joists, about 10cm from the first one.
When either fan is on singly, the noise is not unduly annoying. When they are both on at the same time, the whirr noise changes to a pulsating whirr-whirr-whirr.
I am wondering if the rotating motor parts are interfering with each other electro-magnetically (excuse me if this is the wrong terminology.) If so, it would be fairly straightforward for me to create an extra shelf, say 1m away, and move one fan to give greater separation.
Any thoughts welcome.
Derek

 

[flameport]

Probably caused by the vibration from each motor being slightly different, the pulsing heard is the difference in frequency between the two.
Rubber mounts or fixing each fan to a separate shelf should fix the problem.

 

[kered10]

Thank you, I'll probably try the separate shelf.
Derek

 

[ban-all-sheds]

https://en.wikipedia.org/wiki/Beat_(acoustics)

 

[kered10]

Thanks again. I've moved the fan and it seems to have cured the "beat." It has increased the noise from the fan in the room it is now above, though this is not critical, but I might add rubber mounts later.
Derek