Question about a Hampster?

Here recently for about a month I bought a cage for my hampster that has a wheel at the top of the cage that spins when they run it in. The wheel has a platform underneath it and there is this yellowish brown liquid that is on the platform. I keep my hampsters cage very clean all the time. He isn't acting any different he is eating well and drinking water. Now im not certain that its a male because he wont stay still long enough for me to check but it looks like there is no scrotum there. It looks to me like diarrhea or throw up and thats the only place i ever see it. In the compartment in the top I always see little turds...lol Does anyone know what it could be?