recording cassettes giving a buzz sound

My MacBook pro, late 2015 model, with audacity 2.1.0 installed from dmg installer.
i obtained a RCA to 3.5mm audio cable connected to the amplifier terminals at back-(out section). The RCA is connected to an imic which is connected to the laptop.
In preferences of audacity, i selected for recording the imic USB audio and playback is left at Builtin output. The recording level is 0.1 and keep the volume of amplifier to 2. When i press record and as yet the cassette isn’t playing the the tape, it records a buzzing sound. Then once the voice starts, you can hardly hear it above the buzz. I have used audacity to record vinyl records with no problems. What am I doing wrong ?
Thanks Heather

Is iMic set to Line? Have you tried Line Out or Headphones of the cassette deck?

Are the cassette deck and computer plugged into different power strips or different power outlets?

The current Audacity is 2.1.2:


when i set it to line on imic i found nothing recorded. i then set it to mic and got the sample. i will try the other suggestions. thank you

Line is the correct setting on the iMic. The Mic setting would be expected to distort or hum, because it is providing amplification that is already provided by the cassette deck.