Wesley wrote:
It starts a few minutes after bootup. If I touch the casing it abates or
stops only to start again a few minutes later. I have a feeling its the fan
as I had a similar problem with a PC some years ago.

Is there an easy cure short of replacing the fan?


If it is just dirt, cleaning may help(air in a can etc...).
If the oscillation is due to bearing abrasion... replace it.

Fan failure is directly related to RPM and bearing type.
High RPM and sleeve bearing cause early failure.
Low RPM and ball bearings last longer. Get one of those if you want your
peace... assuming the heatsink can handle the heat with less airflow.