Pedal Problem or Tube Amp Issue?

Hi, in what's perhaps the stupidest thing you've read/heard in a while on here, I have an issue I would like help with. Basically, I've started noticing that whenever I use my SolidGold FX Surf Rider III reverb on a longer setting, there's this irritating crackling/hissing that follows the tail of the reverb. It's kind of like clipping in a sense, but it only ever happens when that specific pedal is on. When I'm playing any other pedal at the same volume, there's no sign of this sound, unless I'm cranking the gain or using drive. This isn't meant to be some lo-fi pedal like say, my Reverberation Machine.

I wasn't sure whether my tubes were on the way out and it would be a case of the pedal emitting frequencies that my amp can no longer handle, or if it was just the pedal. It's supposed to be a real clean drippy surf reverb. I can't grasp why it's suddenly started doing this, and why it only seems to happen with this pedal.

Here is what I'm hearing. https://soundcloud.com/ryan-carrier-963524297/hiss

Apologies if this is moronic. I just wanted a second opinion. I've had the amp (Vox AC4-112) for about a year now, and never replaced the tubes or fiddled with it at all. I do use pretty noisy pedals and I figured maybe I could've worn them out?