Couchbase has a few background tasks which run periodically, however nothing which by default is every 105 minutes. The main tasks are:
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The Expiry Pager (Couchbase Admin Guide) which actually delete any items which have expired from disk. It runs by default every 60 minutes but can be adjusted.
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Compaction (Database and View Compaction is performed to compact the on-disk files, essentially removing deleted / old versions of documents. By default this runs when fragmentation of data / views reaches a given threashold and so the exact time this is run will vary depending on your workload.
In your situation I would guess that your disk/index fragmentation is hitting 30% (the default threshold to start compaction) every 105 minutes, and this is contributing to the load average you see. This is a normal, automatic process and so shouldn’t be a concern. There’s more detail on compaction in the link above.