Hayward Pump Humming/Buzzing

If I shut off my skimmer line (or vice versa with my main line) would that tell me if there was an issue with a leak or something jammed in any of the lines? I mean everything was working fine on Monday when the motor on the old pump went. So I doubt it could be either of those 2 things.
 
Ok so it is not priming.

Did you replace the diffuser o-ring?

You might pull the motor out and make sure everything was installed properly. The problem is most likely due to the work on the motor.
 
Problem solved! I'm an idiot. I never replaced the actual diffuser. I'm looking for that o-ring and noticed the diffuser was still sitting on my work bench. Sorry to have bothered you with my stupidity but thank you so much for your help.
 
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