HDMI to Display port adapter oddity

[Trucker]

I had a fairly noticeable rumble in my receive audio( 8000DLE) that I almost thought was my "new to me" Tannoy powered studio monitors. I had purchased a cable suggested on the forum to go from a TRS (stereo) 3.5mm to split XLR connectors for each speaker. I ran that for a couple of days and then the i7 6700 Dell desktop I was using decided to die. I took it by the shop I bought it from thinking the power supply was bad. It wasn't. It was the motherboard itself. While there, I purchased a Dell OptiPlex i7 9700. I picked up both computers earlier this week. I did a fresh install of Thetis on the OptiPlex, and everything seemed to be working fine. But, there was a rumbling to the receive audio even at a low volume. Nothing I could do would get rid of it. I switched back to the older pc, ( the shop owner put my memory and SSD drive etc. in another i7 6700 desktop he had) and experienced the same problem. Rumbling audio. The Optiplex only has Display Port video out. So, the shop owner gave me a Display Port to HDMI adapter cable so I could use my existing monitor. After going back and forth between the two pc's (here's the important part) I finally realized that I was still using the adapter cable as the older pc also has two Display Port , ports, along with an HDMI port.
The last time I switched back to the older pc with the HDMI port, I replaced the adapter cable and used a regular HDMI to HDMI cable. Started Thetis and the rumble was completely gone! Even at full volume it's not there. I would have never thought there would be a problem like that one.
Anyway, I thought I would share this in case someone runs into a similar problem. ( I did search the forum and did not find any posts with an issue like mine. )
James
WD5GWY

[Trucker]

A quick update. I purchased another Display Port to HDMI adapter on Amazon ( very short cable between adapter and HDMI cable input) and so far, no rumbling in the audio.
James
WD5GWY