Wierd noise from dash or engine compartment

Had my 2000 Cherokee with the 4.0l out for a drive yesterday. About 3 or 4 times my wife and I heard a noise that almost sounded like a bad heater blower motor. Turned it and the Ac off and still heard the noise a couple of times, never lasted more that a minute or two with long pauses in between. Have not been able to pin it down, nor get it to happen when when I had it back in the pole barn. I'm open to any and all suggestions and or help. At this point I'm leaning towards the idler pulley as it seems to be somewhere from the center of the car towards the driver side.
Thank you in advance for any help.
Bill

electric fan...?

You may be hearing the Leak Detection Pump (LDP).
Normally, it is only active on cold starts.
The pump temporarily pressurizes the evaporative emissions system and fuel tank and then measures the rate of leakage, to determine if the system is working correctly.
At the end of the test, the pumps turns off and the evaporative system is then restored to its normal operation.
If the leakage rate is too high, a CEL will be set.