I had a the same problem and went into the dealer back in April. They lubricated the bushings but did not replace because apparently there was a similar problem with the Mazda 3s and a permanent fix ie new bushing was being developed, for both the 3 & 5. Fixed the noise for about a month then it was back. I'm anticipating that the bushing you had done in March was not the expected replacement.
Coming in every 6 months to have this replaced is just not acceptable. Anyone know if a permanent fix is available.
On a side note has anyone had their freezing sliding door locks mechanisms replaced. Same story from dealer here, a fix was in the works - both these fixes have been in the works for over 6 months!!!!!