[LAU] in search of IR response files

I am looking for response files for ir.lv2 - the only convolution reverb so far I have found working within ardour. Looking for natural, long, lush reverbs and thought to have found a good starting point with openairlib.net. However, all big reverbs I've found so far, do produce lots of kind of rythmic clicking (or audible transients) during playback, thus rendering them unusable. The shorter ones partly work, but I just happen to be looking for large spaces. Cathedrals and the like. Why not the whole universe? Any sources or hints, what I may have to look out for? Wrong file format? Or what I may be doing wrong otherwise? It does not seem to be a CPU or load issue at all. And the settings I have been playing with did so far not affect the issue notably. Any ideas? Thanks