Hey HT just working out the kinks on my h2b ek and its developed a weird low idle noise. its not always there and im not driving the car currently. i took a video of it it only makes the noise at low rpm, no knocking if i hold the revs above 1500 and nothing up to 4000, just when it drops back does does the knocking resume, any ideas on what this could be?

 

so i tried pulling spark plug leads to try to isolate the sound, it gets worse on all cylinders as the leads are pulled