There is always going to be a certain amount of pawl clicking in a hub just like there is going to be clicking from a freewheel when coasting. It's inherent in the design. If it is excessively loud there might be a lubrication issue which would require a rebuild and re-grease. The old Sturmey-Archer 3-speeds were noted for signalling the need for a few more drops of oil by an increase in the volume of the clicking.
No IGH is going to totally silent.
For general internal hub information there is no better source than Hubstripping, though it's old.
or of course there's a little info from Sheldon Brown - http://www.sheldonbrown.com/nexus.html
Unfortunately they don't have specific info about the Nexus / inter-7 internals. John Allen may have some other info but I can't find it right now. I think the 7 speed is not made anymore but it is still available here and there. It was a nice even hub design with 244% range, like an old 10 speed roughly.
The Nexus/Inter-8 (AKA Alfine 8 when it has a disc brake) has 4 speeds then shifts up to an overdrive and has the same 4 speeds again. Maybe the 7 speed does something similar. There is a harder shift between 4th and 5th on the 8 speed so if you notice something like that perhaps it explains the clicks in upper gears. I agree that the clicks are probably normal if the thing seems to be shifting and pedaling all right. Think of the old 3 speed clicky Sturmey Archer hubs. Is it newish or could it need new grease inside? They get clickier as the grease gets older. They use a special Shimano grease I think, not a usual home job to replace it.
Shimano also changed the design of the later versions of the 8 speed hubs to use roller bearings or something instead of pawls. The 7 speed came before, so it probably does use old-school pawls.
You should enjoy having one of the most evenly spaced, well thought out internal hubs for general riding and nevermind the little clicks.
Is it possible that the clicking is in 5th and 7th only? Their second stage uses a different sun gear than the others. Look at http://john-s-allen.com/gearing/hubratios.htm.
The Hubstripping site is decent for repository of technical documents and manuals but I have to take the advice as far as gearing and step sizing/spacing with a grain of salt.
When one is dealing with limited choices/options in the number of ratios available compared to modern cartridge derailleur systems and 3-chainring fronts there are going to be inevitable compromises. There aren't 30+ steps available in an IHG.
The types and degree of these compromises start to become a matter of opinion as to what is more important in different situations for different types of riders and conditions Marco seems to be fixated on fixed and even steps and doesn't seem to value bailout gears at the peripheries of the spacing or engineering issues that create slight variations to the ideal. His comparison tests of various hubs seem to only focus on graphs and maps of ratios and take nothing else into account such as quality of materials, internal drag, longevity and ease of repair -among other considerations.
We got one bike from the manufacturer (Azor) with the evil disc lookalike just removed. I bet you could put a big O-ring in the gap, or maybe just silicone the little gap carefully with clear caulk and stop the rattling. I know the sound you mean, but it didn't ever bother me until you mentioned it...
Jeff Schneider said:
Another Shimano noise (OK, this is a bit off topic) that is also not harmful is the rattling of the cooling disc on their roller brakes when riding on rough surfaces. This I've always found really annoying, but I don't have a clue what to do about it...