Could be your aircon cutting in - the pump is at the front of the engine driven by fanbelt with a magnetic clutch that comes in with a click, it also has an idle up solenoid on the bulkhead plumbed into the back of the chargecooler and the inlet manifold. Clamping one of these pipes or disconnecting & blocking would prove.
If it's regular and predictable, but not full time I doubt it's a leak.
The other idle up is the power steering which is a mechanical valve on the bottom of the power steering pump. These usually break or clog with oil. Again, clamping or removing a pipe would confirm, but I doubt this is your problem.
Only other suggestion would be a problem in the idle up valve, but again it doesn't fit symptoms too well,.
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