Whirling sound when kar is cold

When I first startup my kar and push down on the clutch, I hear a whirling sound coming from the trans most likely. When I take my foot off the clutch and the car is idling every is normal. When the car is warmed and I start driving the whirling sound goes away. The kar runs perfectly normal, no problems shifting etc. Thanks in advance for help. Eric.

Is there something specific I should look for to figure which it could be. Also, do you think at some there a chance the problem gets worse and the kar becomes undriveable. thx