96 Rodeo Noise

We just purchased a 96 Rodeo with over 100,000 miles. We replaced timing belt and water pump. Didnt put in tensioner. Now once it warms up the engine makes a slight "diesel" noise at idle only. Any ideas what it is? Could it possibly be from the tensioner? Was hard to push back the plunger on the tensioner.

Yes, it could be. When you pushed the tensioner piston in, did you hold it there with something? Forget to remove whatever was holding it? You could dig back into it and run the engine with the covers off and drive belts removed to confirm if the noise is the tensioner.