Siglent SDS1204X-E trigger affects input signal

[andorrr]

Dear EEVblog Forum,

This is my first post. Attached, you see two screenshots of a Siglent SDS1204X-E scope displaying a 1kHz sine wave originating from a HP8903B Audio Analyzer. The sine wave's THD+noise is close to -90dB, so it is quite a clean signal. It was fed to channels 1 and 3 of the scope, and terminated properly with 50 Ohms. (The HP8903B can be switched to 50 Ohm output impedance).

The only difference in the screenshots' setup is the trigger source. I captured these shots because I noticed in the past days that at such a small horizontal time base, you can see a small bump on the signal at the trigger point. Has anyone else noticed this behavior? I didn't find this on the forum, but please tell me if I am repeating someone else's post. Thanks a lot!

Andor