Please move this discussion to the 'Netflow Traffic Analyzer' forum
Which version of NTA are you using? Assuming you are still using 3.x version of NTA (which is most likely the case), this is likely due to the constant data aggregation process. NTA v4 would definitely alleviate this to a very large degree since NTA v4 uses a Flow Storage DB to store the flow data as opposed to the MS SQL database. NTA v4 will still use the MS SQL database, but the traffic volume would be nowhere near the volume it would generate in 3.x versions. You can read about NTA v4 below to plan your upgrade
SolarWinds Knowledge Base :: NTA 4.0 Installation: Frequently Asked Questions