2x 51.3dB for fans 2x 30dB for PSU so ~55dB.
I think you may be in error with this, as it appears the S7's are using the S5 fans, and the S5 fans are quite loud in the ~70dB range.
If I had any reason to think the S7's were capable of running at ~55dB, I probably would have purchased one to replace a bank of older miners, as that would be quieter than the S5's.
I believe they are using S5+ fans not regular S5 fan's. And I could be wrong on that.
But I think they kept S5+ fans.