siamese

I am a newbie based in Suffolk uk who purchased a new HEQ5 mount recently with Rowan belt modification. I noticed a thump/ bump at one point in the RA axis with clutch loosened off when turning and suggest this could be due to poor castings of mount with bearing casing rocking in casting at a particular point when RA is turned'? The bump is too heavy to be a worm or gear problem in my opinion particularly with clutch loosened off. The HEQ5 mount is solidly made but not up to an "optic quality"!