Trying to record voicemail but the sound is very distorted

So basically I'm trying to record a voicemail, and in it I want to put music for a bit (a rick roll to troll my friends). When I record the voicemail and press play and record my computer audio, the result is very muffled and the volume keeps fluctuating. I tried recording from a speaker but I still can't get it to work. I don't think it's a speaker problem because when I talk the recording is fine. Anyone help?