I know it is an old thread but I thought I would add my experience here also since the Ultimate II+ was mentioned.
I have my WiModem connected to the same C64 that I have my new Ultimate II+L cart plugged into.
I did not notice it immediately, and at first, I wasn't even sure where it was coming from. I said to myself "Oh, that sounds a lot like the old WiModem noise I have heard on other C64s I've used it with. But wait, it isn't not coming through the external speakers connected to the A/V port! It is coming from the UII+L's built-in speaker!"
I confirmed it was the UII+L speaker when I went into the settings and set the speaker audio to OFF. Of course, I do not get the drive sounds this way. I also disabled both of the UltiSIDs since I am not using the UII+L's audio connector. It was the speaker setting alone that made the difference.
Just wanted to mention this one as it doesn't seem to have anything to do with the audio ground issue that was noted in the past. It is interference from the WiModem and the UII+/L built-in speaker.
To be honest, I do not need to have these two devices paired up for the long term. I will usually take advantage of the UII+'s SwiftLink emulation instead.
I have my WiModem connected to the same C64 that I have my new Ultimate II+L cart plugged into.
I did not notice it immediately, and at first, I wasn't even sure where it was coming from. I said to myself "Oh, that sounds a lot like the old WiModem noise I have heard on other C64s I've used it with. But wait, it isn't not coming through the external speakers connected to the A/V port! It is coming from the UII+L's built-in speaker!"
I confirmed it was the UII+L speaker when I went into the settings and set the speaker audio to OFF. Of course, I do not get the drive sounds this way. I also disabled both of the UltiSIDs since I am not using the UII+L's audio connector. It was the speaker setting alone that made the difference.
Just wanted to mention this one as it doesn't seem to have anything to do with the audio ground issue that was noted in the past. It is interference from the WiModem and the UII+/L built-in speaker.
To be honest, I do not need to have these two devices paired up for the long term. I will usually take advantage of the UII+'s SwiftLink emulation instead.