Sorry - Another puncture question...

piedwagtail

Bit embarrassing having to ask for help with punctures but this has me baffled so here goes...
Sorry if this is a bit long, just want to get all the details. If tl;dr applies see the bottom.

A bit of background to start off:
The winter bike has 28c Panaracer Paselas on cheap, heavy but bombproof hybrid rims, which take a Schrader valve.
Bought 4 new Schwalbe tubes in 18-28
I run them at 100psi, the limit on the Paselas is 105psi. I leave tyres pumped up if that makes a difference rather tha pumping before every ride. I'm always check the tyre is seated properly after a pretty nasty blowout.
Not had a single puncture out on the road. Front wheel completely fine.

The rear wheel on the other hand...
First new tube goes in during the build; fine for 2 days, still hard when I got back from the last ride, next morning its flat.
The hole is a pretty big tear (7-8mm) not going all the way through the rubber, with a round hole in the middle, on the inside of tube not far from the valve (right on one of the raised bits of rubber from vulcanizing process)
Check the tyre: nothing. Check the rim: no protruding spokes, rim tape fine, seated properly etc.
Wipe everything down and put tube number 2 in. Repair tube 1 for use as spare.
Two or three days later: same thing and tube 2 goes down in the night, on the 'seam', inside of tire etc.
Repeat previous checks again... All good as before. Tube 3 goes in and 2 repaired as spare...
Four or five days go by this time so I'm happy alas the next morning the process is repeated...

Had even longer this time around, probably a couple of weeks, witnessed it this time, as I was downstairs, no warning it just starts hissing and goes flat. Inside of the tyre again. Nothing wrong with the tyre or rim again. Not on a raised 'seam' this time but the tear seems to follow a line in the tube.

So, baffled by this. Annoying as I usually only notice in the morning when I want to be getting ready to ride or go to college instead of fixing punctures.

Anyone with similar problems? Ideas for causes or solutions? Dodgy batch of tubes as I got them together?

Thanks in advance everyone.

If tl;dr
Three punctures in 3 brand new tubes. All on the inside. Rims, tape and tyres all fine and sharp object free.
Any ideas??

desweller

Are you sure the rim tape is OK? I know you say you've checked it but it only needs to fail to cover a small section of one of the holes in the rim to cause a failure.

toasted whippet

Either rim tape as said above, a bit of rough metal inside the rim, or you are pinching the tube under the wired bit of the tyre when you put the tube in.
When you put the tube back under the tyre DO NOT leave the tube flat. Put just enough air in the tube to give it some shape, THEN insert it under the tyre. Reseat tyre properly. Push valve back into tyre to make sure that doesn't pinch.
Having some air in the tube stops a small part of it pinching under the wire, and then holing overnight under pressure.
Reinflate. Jobs a good'un.

piedwagtail

Thanks for the replies guys.

Rim tape covers every hole with some to spare. None of the spokes protrude from the nipples and they're all well below the level of the second wall. No rough metal that I can find although I'll check again.

I do inflate the tube already and push up on the valve etc. so I don't think its being pinched, although I guess I'll have to extra careful in future. The tube does tend to sit quite low in the tyre when I first put it on but I spend as long as it needs to get it all seated nicely before I ever start to put and high pressure into it. I do wonder whether the tubes just don't like expanding quite so much as deflated they're only as big as a tube for 23c tyres.

I think I'll get some different inner tubes in 28-37c and see if the problem persists.

Cheers again guys