Noise showing in recordings

Hi all.
I found some old cassettes and my mom and I wanted to digitize them, so we could them have copies and not lose them. Well I started to record them when I noticed this sound that was showing in the previews and is now showing in the recording itself. I’m certain its not from the tapes but the play or cable we’re using. I took a sample from a blank side, and using “Noise removal” in Audacity hasn’t changed it. Any ideas?

Noise-removal won’t remove pulses like that.

Frequency of the pulses is very consistent [10Hz], but with varying amplitude :
so it’s consistent with radio-interference, ( cell phone ? ).

Well a cell phone was in the room, should I turn it off? The reason I cast doubt on the phone was because the pulse only seems to show when I hit the play button. Once I turned the tape player off the sound stopped right away. Still I’ll take the cell phone out of the room and turn it off just to make sure I can cross it off the list as possible reason for the pulses.

It might be the interface. Are you using a mixer? There are filters and boosters available to clean up noisy signals, even if generated by non-pro equipment.